1. Field of the Invention
This invention relates to a pH sensor for continuously measuring the pH of a test solution, such as in industrial applications.
2. Description of the Prior Art
A wide variety of kinds and types of pH sensors have been used for industrial applications. They are, for example, classified according to the manner in which they are used, such as continuous flow type, immersion type, and submersion type pH sensors. The construction of the sensor is grouped roughly into single purpose and composite types. In addition, pH sensors include liquid junctions either with or without a KCl solution supply.
The various forms of pH sensors are needed to meet different conditions in which the test solutions are available for measurement. Those pH sensors which are best suited for the various test solution conditions are selected for best results. Having pH sensor structures which are different for single or composite pur- poses, however, is disadvantageous in terms of expense of fabrica- tion and expense of maintenance.
The pH sensors usually include electrodes having a detecting end which can be cleaned by a cleaning unit mounted on the pH sensor. The cleaning unit usually comprises a brush positioned immediately below the electrode or sensor unit of the pH sensor. The brush can be rotated by a motor while the brush is being brought into contact with the sensor unit, to scrape deposits off the sensor unit. With such a conventional cleaning unit, the deposits which are scraped off the sensor unit, are then attached to the brush. Disadvantageously, this shortens the service life of the brush. Since the brush is electrically powered for rotation thereof, the seal and power transmission mechanism which are used therein, are complex and hence make such prior cleaning unit expensive.
There are also known various other cleaning units for cleaning pH sensor units or electrodes. They include, for example, ultrasonic cleaners, jet cleaners, and brush cleaners. These cleaning units have their own advantages and disadvantages, and are selectively used to suit the kind of solution which is to be measured. The pH sensors of the continuous flow type, immersion type and submersion type, are equipped with varying cleaning units of their own unique design, and are hence incompatible with each other. Furthermore, cleaning units which operate on different cleaning principles, cannot be used with pH sensors which may however, be used in the same type of use, such as continuous flow, immersion, or submersion.
Accordingly, there exists in the art a deficiency in pH sensors, which needs to be fulfilled.